This application claims the priority of German Patent Application No. 197 56 988.9, filed Dec. 20, 1997, the disclosure of which is expressly incorporated by reference herein.
A glow plug is used in Diesel engines in the combustion chamber for preheating during cold starts or as a glow pencil in the intake manifold for preheating the intake air. The glow plug or glow pencil consists of a corrosion-free metal jacket, a heating and regulating coil, and an electrically insulating compressed powder filling. The heating and regulating coil consists of a ferritic steel in the heating area, to which a pure nickel wire is soldered as a regulating resistance.
The material of the heating coil is subject to thermal and chemical influences that can adversely affect the lifetime of the glow plug. At the least, these influences constitute important parameters for the service life of the glow plug. Intercrystalline corrosion can occur which is promoted by crystal growth and a tendency toward coarse grain formation in ferrite heating conductors. In addition, at high temperatures there can be corrosion at the free surface of the heating coil and hence reduction of the cross section of the heating wire can occur. This process is made possible by the presence of oxygen which has been absorbed on the particle surface of the powder filling from the air during the manufacture of the glow plug.
The goal of the present invention is to provide a glow plug that has a heating coil with a long lifetime. According to the present invention, during the operation of the glow plug, the residual oxygen is bound by an integrated oxygen getter. Further, an inert atmosphere is maintained in the pores and on the free pore surface of the filling. Any corrosion processes of the type described above are therefore suppressed or proceed extremely slowly at most. Glow plugs equipped according to the present invention therefore have a considerably longer lifetime than before.